In the research of semiconductor coatings, memories, and displays, the precursor molecule plays an important role to obtain high quality thin films. It controls many parameters such as conformality and affects physical and electrical properties of thin films. The precursor molecules require high purity, high thermal stability, high volatility, appropriate reactivity, and low toxicity. Additionally, in processes of thin films, the precursor molecules should vaporize in a limited time and at a reproducible rate for Chemical Vapor Deposition (CVD) or Atomic Layer Deposition (ALD).
In semiconductor areas, Group 5 transition metal-containing films have long been utilized for a variety of applications. The resistance switching characteristics of MxOy thin films show its potential applications for the next generation nonvolatile resistive random access memory (ReRAM) devices as well as for high-k capacitor applications such as a thin layer in-between ZrO2 layers to reduce leak current and stabilize the phase.
Typical Group 5 transition metal halides have been explored for the deposition of MxOy (M=Nb, Ta; x=1-2; y=1-5) by CVD or ALD. Those precursors, mainly NbCl5 or TaCl5, may require high deposition temperatures and are sometimes not appropriate as precursors due to etching effects and precursor residues. Chem. Vap. Deposition 2009, 15, 269-273; Thin Solid Films, 1999, 111).
Nb(OEt)5 has shown promising results to deposit amorphous Nb2O5 by ALD with a stable temperature windows of 230-260° C.) (Chem. Vap. Deposition 1998, 4, pp. 29-34). In addition, the precursor has been used to study the mechanism of NbxOy ALD depositions using H2O or D2O (Langmuir 2010, 26(2), pp. 848-853).
In case of Ta(OEt)5, ALD of Ta2O5 with H2O has shown a process window between 170° C. and 230° C., having amorphous phase at 600° C., as deposited and crystalline phase at 800° C. (Microelec. Eng. 2010, 87, pp. 373-378).
Imido-type precursors are known and used to deposit Group 5 transition metal containing films. They are mostly in a liquid phase with high vapor pressure, which provide an advantage for vaporizing and transferring to a reaction chamber. Many derivatives have been studied for CVD (Chem. Vap. Deposition 2008, 14, pp. 334-338; Chem. Vap. Deposition 2000, 6, pp. 223-225; ECS Trans. 2008, 16 (5), pp. 243-251) or ALD (Chem. Mater. 2012, 24, pp. 975-980). However, those precursors showed limited ALD temperature windows with a maximum of 275° C.
Other similar structures with mixed ligands of Group 5 transition metal have been described, such as V(=NtBu)(NiPr2)(OtBu)2. Zeitschrift fuer Anorganische and Allgemeine Chemie (1997) 623 (8), pp. 1220-1228, but have not considered for thin film applications.
A need remains for novel group 5 transition metal-containing compounds suitable for vapor phase thin film deposition.